Electromechanical actuator driven governor for ram air turbine

ABSTRACT

A ram air turbine governor includes a hub carrying multiple turbine blades. A sensor is configured to detect a parameter. A counterweight is coupled to at least one turbine blade and is configured to provide an input to the turbine blade in response to a centrifugal force to move the turbine blade from a first pitch position to a second pitch position. An electromechanical actuator is operatively coupled to the counterweight. A controller is in communication with the mechanical actuator and the sensor. The controller is configured to command the electromechanical actuator and move the turbine blade from the second pitch position to a third pitch position in response to the detected parameter.

BACKGROUND

This disclosure relates to a ram air turbine system. More particularly, the disclosure relates to a speed governor for the ram air turbine system.

A ram air turbine (RAT) system includes turbine having blades. A typical RAT has a governor that adjusts the pitch angle of the turbine blades over the speed range of the aircraft. The turbine blades control the output rotational speed delivered from the blades to an electrical generator and/or hydraulic pump that are designed to operate efficiently over a typical operating speed range.

One type of governor includes a set of springs which acts against a set of counterweights to set a desired blade pitch angle. The springs are often large and only operate on the principle of mechanical force balance with the counterweights. In these types of systems, there is no external mechanism to set the blade pitch. Other blade pitch control governors have been developed that entirely eliminate mechanical control systems that incorporate counterweights.

SUMMARY

A ram air turbine governor includes a hub carrying multiple turbine blades. A sensor is configured to detect a parameter. A counterweight is coupled to at least one turbine blade and is configured to provide an input to the turbine blade in response to a centrifugal force to move the turbine blade from a first pitch position to a second pitch position. An electromechanical actuator is operatively coupled to the counterweight. A controller is in communication with the mechanical actuator and the sensor. The controller is configured to command the electromechanical actuator and move the turbine blade from the second pitch position to a third pitch position in response to the detected parameter.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be further understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a perspective view of a RAT system in a deployed position.

FIG. 2 is a perspective view of an example RAT system having a mechanical governor assembly and an electromechanical actuator.

FIG. 3 is a schematic of an example RAT control system for the disclosed RAT system.

FIG. 4 is another example RAT system having the mechanical governor assembly and an electromechanical actuator.

DETAILED DESCRIPTION

FIG. 1 illustrates a RAT system 10 secured to an aircraft structure 12 by a housing 14. The housing 14 pivotally supports a strut 16 supporting a case 17 at one end to which a turbine 18 is mounted. The turbine 18 includes blades 20, which impart rotational drive to a generator 22 and a hydraulic pump 26. An actuator 24 is interconnected between the strut 16 and the housing 14. The RAT system 10 is illustrated in its deployed position.

An example RAT system 10 is illustrated in FIG. 2. The blades 20 include a root 28 that is supported by the hub 19 by a bearing assembly 30. The blades 20 are rotatable about their respective pitch axes. A counterweight 32 is coupled to each of the blades 20, which bias the blades 20 from a first pitch position to a second pitch position in response to a force input due to the centrifugal forces on the counterweights 32. In one example, the first pitch position corresponds to a fine pitch, and the second pitch position corresponds to a coarse pitch. The turbine 18 rotates at its maximum speed in the fine pitch position. Thus, the counterweights 32 govern the turbine speed by rotating the blades 20 to a coarser position as the speed reaches a predetermined threshold. Rotation of the hub 19 rotationally drives a drive shaft 50, which in turn rotationally drives the generator 22 and pump 26.

A yolk plate assembly 34 cooperates with the counterweights 32. In particular, a cam follower 36 provided on the counterweights 32 is arranged between first and second spaced apart members 42, 44 of the yolk plate assembly 34. The yolk plate assembly 34 moves linearly along guide pins 38 with rotation of the blades 20. The yoke plate assembly 34 is affixed to a centrally located governor shaft 40.

A spring assembly 46 is arranged within a nose cone 48. The spring assembly 46, which includes a pair of concentric coil springs in the example, applies a spring force on the yolk plate assembly 34 to counteract the centrifugal force created by the counterweights 32. In this manner, the spring assembly 46 establishes a limit to the overspeed protection provided by the counterweights 32. Such an arrangement provides overspeed protection of about ±10-20% of an overspeed design limit.

An electromechanical actuator 52 is coupled to the governor shaft 40 to linearly move the yolk plate assembly 34, which changes the pitch of the blades 20 to a third pitch position. A coupling device 54 is used to mechanically interconnect the electromechanical actuator 52 and the governor shaft 40, if necessary. The electromechanical actuator 52 may be an acme screw, ball screw or other configuration that enables the use of a relatively small motor and prevents back-driving. The electromechanical actuator 52 may be powered by the generator 22, in one example.

The electromechanical actuator 52 communicates with one or more sensors and is used to increase (fine direction) or decrease (coarse direction) the pitch of the blades 20 in response to detected parameters from the sensors. For example, the electromechanical actuator 52 may refine the overspeed limit and/or manipulate the pitch of the blades 20 during other conditions, such as turbine start-up or blade vibrations.

A schematic of a RAT control system 56 is schematically illustrated in FIG. 3. A controller 58 communicates with the electromechanical actuator 52. The blades 20 are subject to a blade pitch force 66 due to the RAM airflow over the blades 20. This blade pitch force 66 is altered by a counterweight force 68, which is limited by a governor spring force 70, if governor springs are used. The electromechanical actuator 52 provides an input to the blades 20 to move the blades from the second pitch position to the third pitch position thereby commanding the blades 20 to a position other than that dictated by the force balance on the blades (i.e., airflow over blades, counterweights and, if used, governor springs).

A speed sensor 60, a condition sensor 62 and/or a vibration sensor 64, for example, are in communication with the controller 58. The speed sensor 60 may be indicative of air speed or the rotational speed of the turbine 18. In one example, the speed sensor 60 is provided by speed sensor integrated with the generator 22. The controller 58 is programmed to command the electromechanical actuator 52 to position the blades 20 such that the target overspeed limit is reached.

The condition sensor 62 may be a sensor that detects a turbine start-up condition, such as deployment of the RAT. In one example, the condition sensor may be a switch that initiates RAT deployment. The controller 58 is programmed to command the electromechanical actuator 52 to position the blades 20 initially to position in which the hub 19 rotates most rapidly up to desired operating speed.

The vibration sensor 64 is configured to detect undesired vibration in the RAT, for example, blade vibration. The controller 58 is programmed to command the electromechanical actuator 52 to position the blades 20 to a position that induces less vibration, for example, to a coarser blade pitch.

Another example RAT system 110 is illustrated in FIG. 4. The blades 120 are mounted on the hub 119. The counterweights 132 automatically rotate the blades 120 from a first pitch position to a second pitch position in response to centrifugal force on the counterweights 132. The yolk plate assembly 134 is coupled to the counterweights 132 via the cam followers 136. The coupling device 154 interconnects the governor shaft 140 and the electromechanical actuator 152. The electromechanical actuator 152 is arranged in the nose cone 148 instead of the case 117, as illustrated in the example of FIG. 2. The electromechanical actuator 152 may be easier to package in the nose cone 148, for example, and the governor springs may be eliminated.

Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine their true scope and content. 

1. A ram air turbine governor comprising: a hub carrying multiple turbine blades; a sensor configured to detect a parameter; a counterweight coupled to at least one turbine blade and configured to provide a rotational input to the turbine blade in response to a centrifugal force to move the turbine blade from a first pitch position to a second pitch position; an electromechanical actuator operatively coupled to the counterweight; and a controller in communication with the electromechanical actuator and the sensor, the controller configured to command the electromechanical actuator and move the turbine blade from the second pitch position to a third pitch position in response to the detected parameter.
 2. The ram air turbine governor according to claim 1, comprising a yoke plate assembly coupled to the counterweight and movable linearly with rotation of the blades.
 3. The ram air turbine governor according to claim 2, comprising a governor spring cooperating with the yoke plate assembly and configured to provide a force counteracting the rotational input.
 4. The ram air turbine governor according to claim 2, comprising a governor shaft affixed to the yoke plate assembly, and the electromechanical actuator coupled to the governor shaft and configured to move the yoke plate assembly in response to the command.
 5. The ram air turbine governor according to claim 2, wherein the counterweight includes a cam follower coupled to the yoke plate assembly and configured to translate between linear and rotational movement of the yoke plate assembly and the blade, respectively.
 6. The ram air turbine governor according to claim 1, wherein the sensor is a speed sensor, and the parameter corresponds to a rotational speed of the hub.
 7. The ram air turbine governor according to claim 1, wherein the sensor is a start-up condition sensor, and the parameter is a start-up condition.
 8. The ram air turbine governor according to claim 1, wherein the sensor is a vibration sensor, and the parameter is a vibration of the blade.
 9. A ram air turbine governor comprising: a hub carrying multiple turbine blades; a sensor configured to detect a parameter, the parameter including at least one of a start-up condition and a vibration condition; an electromechanical actuator operatively coupled to the turbine blades; and a controller in communication with the electromechanical actuator and the sensor, the controller configured to command the electromechanical actuator and move the turbine blade between pitch positions in response to the detected parameter.
 10. The ram air turbine governor according to claim 9, comprising a counterweight coupled to at least one turbine blade and configured to provide a rotational input to the turbine blade in response to a centrifugal force to move the turbine blade from a first pitch position to a second pitch position. 